Fabrication of polytetrafluoroethylene (PTFE) and some copolymers of tetrafluoroethylene is often difficult, due to the fact that even above their melting points they flow little if at all. Thus typical plastics melt processing techniques are often useless with such polymers. Previous attempts have been made by others to make these polymers more processible, in order to make useable parts.
Thus U.S. Pat. No. 2,685,707 and J. F. Lontz, et. al., Ind. Eng. Chem., vol. 44. pp. 1805-1810 report that many low molecular weight organic compounds such as hydrocarbons and esters can be used as "lubricants" to aid in the forming of parts from particulate PTFE. The lubricants are removed typically by volatilization and/or sintering, and a solid part is produced by sintering the remaining PTFE.
U.S. Pat. Nos. 3,407,249 and 3,679,614 report that porous PTFE parts are produced by mixing particulate PTFE with poly(methyl methacrylate) (PMMA) and other compounds. The PMMA and other compounds can be removed by use of solvents for the PMMA such as acetone.
U.S. Pat. Nos. 2,985,918 and 3,054,761 describe a process for making and using a composition comprising PTFE and PMMA. This mixture may be sintered to volatilize and decompose the PMMA, and to sinter the PTFE, so that a porous PTFE article is produced.
Among the desired properties a material should impart to PTFE in order to help form PTFE parts, are, easy mixing of the components, good green strength of the mixture so parts of the mixture will not deform readily, especially under sintering conditions, and clean sintering of the processing aid (lubricant) so that the remaining PTFE part is free of impurities (e.g., ash and char) and has a minimum amount of porosity. It is the object of this invention to provide such a composition and a process for making and using it. None of the above references teaches the use of poly(2,2-dialkylpropiolactones) as processing aids or lubricants for PTFE.